1. Field
The present disclosure relates to a well borehole seismic sensing system. More specifically, the present disclosure relates to a well borehole seismic sensing system having a plurality of rotatable sensor arrays.
2. Background
Seismic sources and sensors can be deployed in well boreholes for a variety of oilfield operations, including monitoring well operations, fracturing operations, performing “seismic-profiling” surveys to obtain enhanced subsurface seismic maps and monitoring downhole vibrations.
Seismic sensors deployed in well boreholes can be useful in monitoring fracturing and injection well operations, obtaining seismic measurements over time, and creating enhanced subsurface maps and to improve reservoir modeling. Seismic data can include natural seismic data (e.g., from earthquakes), seismic signals generated by conventional surface or subsurface seismic sources, and seismic signals generated by formation fracturing. Presently, the majority of seismic data is gathered by wireline methods or by deploying seismic sensors such as geophones on coiled tubing or production pipe. By way of example, a conventional three-axis geophone can detect particle motion in three mutually orthogonal directions (x, y, and z directions).
Modern petroleum drilling and production operations demand a great quantity of information relating to parameters and conditions downhole. Using this information, the driller can more precisely determine the orientation of the bottomhole assembly and the type of formation through which the bottomhole assembly formation is drilling. The collection of information relating to conditions downhole is commonly referred to as “logging”. In conventional oil well wireline logging, a probe is lowered into the borehole after some or all of the well has been drilled. The probe is used to determine certain characteristics of the formations traversed by the borehole. The probe can include one or more sensors to measure parameters downhole and typically is constructed as a small hermetically sealed steel cylinder for housing the sensors, which hangs at the end of a long cable or “wireline.” The cable or wireline provides mechanical support to the probe and also provides an electrical connection between the sensors and associated instrumentation within the probe and electrical equipment located at the surface of the well. Normally, the cable supplies operating power to the probe and is used as an electrical conductor to transmit information signals from the probe to the surface. In accordance with conventional techniques, various parameters of the earth's formations are measured and correlated with the position of the probe in the borehole as the probe is pulled uphole.
While wireline logging can be useful in gathering information, it has certain disadvantages. For example, before the wireline logging tool can be run in the wellbore, the drill string must first be removed from the borehole, resulting in considerable cost and loss of drilling time. In addition, because wireline tools are unable to collect data during the actual drilling operation, drillers must make some decisions (such as the direction to drill, etc.) without sufficient information. And because wireline logging occurs after the wellbore is drilled, the accuracy of the wireline measurement is questionable as drilling mud begins to invade the formation surrounding the borehole.
These limitations associated with wireline logging have resulted in increased emphasis on the collection of data during the drilling process. By collecting and processing data during the drilling process, without having to remove the drilling assembly to insert a wireline logging tool, the driller can make accurate modifications or corrections in “real-time” to optimize performance, and the measurements during drilling increase the integrity of the measured data.
Other present technology for seismic and micro-seismic data collection within the oil and gas industry relies on an array of geophones, positioned some distance away, inside the wellbore casing of monitoring wells. The location of a monitoring well, or wells, from the target well being drilled, is positioned in a known location suitable for data gathering. But it is difficult to determine the actual position of the geophone array placed in the monitoring well. The positioning of an instrumented array, sometimes totaling fifteen in one string, is unknown inside the borehole. To correct for this unknown position requires a calibrated seismic source(s) to generate a known position. Then, sophisticated algorithms must be used to determine the rotation of each geophone array from the source. Using this method, the data collected during the fracturing process has been shown to have errors.
The borehole sensing systems (BSS) and methods described herein can reduce error and provide improved data collection, resulting in more accurate analysis of a reservoir being fractured. This can be accomplished by locating sensors in the vertical shaft wellbore casing. In conjunction with the monitoring well data, a more precise presentation of azimuthal orientation of a hydraulically propagated fracture can be achieved in the post analysis process.
The BSS is also designed to improve the analysis of the horizontal borehole and provide improved data analysis through software models by providing a quicker “snapshot” of the data collected, through preprocessing, as the sensor data streams through to a memory storage array. By reducing error in the data collection process, analytical results can be improved. The BSS can also provide flexibility in altering data sets in real-time, without altering the stream of data collected. Additional sensors can be installed, providing a triangulation of arrays, which can improve the overall accuracy of modeling the formation over time.